Bidirectional MR Actuator Housing Layout for Off-State Torque Control
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Solution Overview
Problem
Existing bidirectional magneto-rheological actuators face limitations due to off-state force issues, magnetic flux bottlenecks, and increased mass and size, which affect torque generation and haptic feedback performance, especially in applications requiring both pull and resistant torque.
Innovation Solution
A bidirectional magneto-rheological actuator design featuring a housing with both non-magnetic and magnetic portions, rotatably coupled with a magnetic field generation assembly comprising separate coil assemblies to control MR fluid engagement between rotors and the housing, allowing for asymmetric magnetic flux distribution and reduced mass while maintaining structural symmetry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If coils are positioned on side walls away from disc circumference to eliminate magnetic flux bottleneck, then ease of manufacture and maintenance is improved and mass is reduced, but magnetic saturation occurs in thin side walls
Solution Approach 1:
The housing is designed with non-uniform wall thickness, featuring thicker portions at locations prone to magnetic saturation (such as near coil assemblies and magnetic flux paths) and thinner portions where magnetic saturation is less likely to occur. This localized variation in thickness allows the structure to resist magnetic saturation in critical areas while maintaining overall mass reduction and manufacturing ease.
2Weight of moving object
If thin side walls are used to reduce mass, then weight is reduced, but magnetic saturation occurs in the side walls
Solution Approach 1:
The housing employs variable wall thickness with strategically thicker sections positioned to withstand magnetic saturation stresses while thinner sections reduce overall mass. This selective thickening is applied only where magnetic flux density is highest, optimizing the balance between weight reduction and magnetic saturation resistance.
3Adaptability or versatility
If MR brake configuration is used to generate pull and resistant torque, then bidirectional torque capability is improved, but off-state force and uncontrollable torque are present
Solution Approach 1:
The patent extracts and eliminates the source of off-state force by redesigning the magnetic circuit and flux paths. By positioning coils on side walls and configuring magnetic circuits to guide flux through dedicated paths, the design prevents residual magnetic fields from creating unwanted torque in the off-state, while preserving bidirectional torque generation capability.
Solution Approach 2:
The patent introduces magnetic circuits and flux path structures as intermediaries between the coils and the discs. These intermediary elements control and direct magnetic flux, ensuring that magnetic fields are properly contained and directed only where needed, thereby preventing off-state torque while maintaining effective bidirectional control.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design enhances torque generation capabilities, reduces mass and size, and improves haptic feedback by allowing for efficient control of MR fluid rheology, addressing the limitations of previous configurations and enabling effective bidirectional torque application.
Implementation Method 1
Two sets of magnetic coils are wound in an outer cylinder of the housing proximal the circumference of the respective two discs. The coils are exciting independent of each other depending on the desired direction of BMRA. As the power of coil is turned on, magnetic field is generated and the MRF in duct becomes solid-like instantaneously.
Implementation Method 2
Magneto-rheological (MR) fluids has been quickly researched and applied in this area. The essence of MR gloves is a combination of many MR brakes, which block the movement of the fingers in proportion to the actual feedback force. The MRF in duct becomes solid-like instantaneously when magnetic field is generated.
Data Source
AI summary
Disclosed herein is a bidirectional MR actuator comprising a first input member comprising a first rotor, an output member comprising a second rotor and a second input member comprising a housing having a non-magnetic portion and a magnetic portion. Each of the first input member and the output member are coupled to the second input member, the housing defining a chamber for accommodating the first rotor and the second rotor therein and further for receiving a quantity of MR fluid therewithin. The actuator further comprises a magnetic field generation assembly comprising a first coil assembly configured to selectively apply a magnetic field to a portion of the MR fluid between the first rotor and the second rotor, and a second coil assembly configured to selectively apply a magnetic field to a portion of the MR fluid between the second rotor and the magnetic portion of the housing.